Bronchopulmonary dysplasia/chronic pulmonary disease of prematurity (BPD/CPDP) is currently the most significant of the long-term sequelae seen in surviving premature infants, affecting 15 to 35 percent of babies whose birth weight was less than 1500 grams. This entity, diagnosed at one month of postnatal age, is associated with an 11 to 36 percent mortality and a 50 to 69 percent chance of re-hospitalization in the first year of life. All prior studies of risk factors have been descriptive only and have analyzed data abstracted from medical records. The proposed study of BPD/CPDP seeks to identify risk factors, especially those that can be minimized or prevented in two large, high quality databases: one form a randomized trial of phenobarbital prophylaxis for neonatal intracranial hemorrhage (NIH #NS20807) and another from a study of antenatal risk factors for intraventricular hemorrhage in premature infants (NIH #NS20658F). The strengths of these two databases are their extensive catalogues of recent prospectively collected perinatal and neonatal data and their large numbers of infants at high risk for BPD/CPDP. These high quality data provide an ideal source of information for the first controlled study of risk factors for BPD/CPDP, at a cost which is far below the amount that would be required to initiate and implement a new epidemiologic study of BPD/CPDP with data of comparable quality.